Apparatus, method, and computer program for a resolution-enhanced pseudo-noise code technique

ABSTRACT

An apparatus, method, and computer program for a resolution enhanced pseudo-noise coding technique for 3D imaging is provided. In one embodiment, a pattern generator may generate a plurality of unique patterns for a return to zero signal. A plurality of laser diodes may be configured such that each laser diode transmits the return to zero signal to an object. Each of the return to zero signal includes one unique pattern from the plurality of unique patterns to distinguish each of the transmitted return to zero signals from one another.

ORIGIN OF INVENTION

The invention described herein was made by an employee of the UnitedStates Government and may be manufactured and used by or for theGovernment for governmental purposes without the payment of anyroyalties thereon or therefor.

FIELD

The present invention generally relates to a high resolutionthree-dimension (3D) imaging lidar system and, more particularly, to ahigh resolution 3D imaging lidar system using a resolution-enhancedpseudo-noise code technique.

BACKGROUND

Space research in Earth orbit, lunar, and interplanetary environmentshas resulted in an urgent demand for autonomous observing technologiesin recent years. One technique for autonomous observation is based onactive imaging sensors. Active 3D imaging systems are attractive for awide range of applications, such as surface reconstruction, mapping,landing of probes, obstacle recognition and navigation for vehicles,rendezvous, and docking maneuvers.

Much effort has been made to develop a 3D imaging laser radar based on atime-of-flight (TOF) technique. In this technique, a very short laserpulse is sent out towards the object and the scattered light from theobject is collected. The time delay between the start pulse and thereturned pulse is measured to determine the object distance. With thistechnique, a high peak power laser is required. In many cases, arelatively complicated diode pump, such as a passively Q-switchedsolid-state laser, is used as a light source.

However, applications of space-based lidars that require compact size,light weight, and reliability are usually constrained by the lasersource. To date, the smallest devices appropriate for such applicationsare diode lasers. Unfortunately, compact semiconductor lasers have peakpower levels well below the requirements of lidar systems based on TOFtechniques. Thus, a pseudo-noise (PN) coding technique for 3D imagingmay be beneficial.

PN code may include a spectrum similar to a random sequence of bits butis deterministically generated. PN code modulation may be widely used inRF communications. It may typically be modulated in non-return-to-zero(NRZ) format, where the transmitted pulse width equals to the coding bitperiod. Timing measurement accuracy using PN code technique may beproportional to the transmitted pulse width divided by the measurementsignal to noise ratio. Shorter transmitted pulses result highermeasurement accuracy for the same transmitted average power.Traditionally, PN code using NRZ format modulates the signal at 50% dutycycle. PN code modulation using an advanced scheme with a lower dutycycle may substantially increase the measurement accuracy.

SUMMARY

Certain embodiments of the present invention may provide solutions tothe problems and needs in the art that have not yet been fullyidentified, appreciated, or solved by current 3D imaging systems. Forexample, embodiments of the present invention utilize a return-to-zero(RZ) resolution-enhanced pseudo-noise code technique to improve theranging resolution by an order of magnitude with the same transmittedoptical power. The duty cycle of RZ format can be reduced by narrowingthe transmitter pulse width. The sharp transmitted pulses substantiallyincrease the system timing measurements and reducing the backgroundnoise.

In accordance with an embodiment of the present invention, an apparatusis provided. The apparatus includes an array of laser diodes, such thateach laser diode can transmit a RZ signal to different locations on anobject. The apparatus also includes a telescope that can receive each ofthe transmitted RZ signals. Each of the RZ signals includes a uniquepattern to distinguish between itself and the other transmitted RZsignals.

In another embodiment of the present invention, a computer-implementedmethod is provided. The method includes transmitting a return to zerosignal to different locations on an object. The method also includesreceiving each of the transmitted return to zero signals. Each of thereturn to zero signals includes a unique pattern to distinguish betweenitself and the other transmitted return to zero signals.

In yet another embodiment of the present invention, an apparatus isprovided. The apparatus includes a pattern generator configured togenerate a plurality of unique patterns for a return to zero signal. Theapparatus also includes a plurality of laser diodes. Each of laserdiodes is configured to transmit the return to zero signal to an object.Each of the return to zero signals includes one unique pattern from theplurality of unique patterns to distinguish each of the transmittedreturn to zero signals from one another.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the advantages of certain embodiments of the inventionwill be readily understood, a more particular description of theinvention briefly described above will be rendered by reference tospecific embodiments that are illustrated in the appended drawings.While it should be understood that these drawings depict only typicalembodiments of the invention and are not therefore to be considered tobe limiting of its scope, the invention will be described and explainedwith additional specificity and detail through the use of theaccompanying drawings, in which:

FIG. 1 illustrates a system for 3D imaging, according to an embodimentof the present invention.

FIG. 2 is a flowchart illustrating a method for transmitting RZ pulses,according to an embodiment of the present invention.

FIG. 3 is a flowchart illustrating a method for receiving the RZ pulses,according to an embodiment of the present invention.

FIG. 4 is a flowchart illustrating a method for computing the distancebetween the source and the object, according to an embodiment of thepresent invention.

FIG. 5 illustrates a block diagram of a computing system for 3D imaging,according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In order to measure distance between a laser source and a target(moveable or non-movable), a laser pulse is transmitted to the targetand is reflected and returned. The time for the laser pulse to betransmitted and returned allows determination of the distance betweenthe source and the target. However, transmitting pulses in rapidsuccession may cause confusion in delineating the difference between onepulse and another. In other words, if a first pulse is transmitted to atarget and a second pulse is transmitted shortly thereafter to thetarget, it may be hard to determine which pulse returned first, i.e.,the first pulse or the second pulse.

One or more embodiments solve the above-mentioned issue ofdifferentiating between pulses transmitted in rapid succession. Forexample, one or more embodiments of the present invention pertain totransmitting a plurality of PN coded RZ pulses, to an object andcalculating the time elapsed between transmission and reception of theRZ pulses by matching the transmission and reception pulse patterns todetermine the distance between the source and the object. RZ pulse widthcan be a few percent of the PN code bit period. This results in enhancedtiming resolution and reduced background noise.

FIG. 1 illustrates a system 100 for 3D imaging, according to anembodiment of the present invention. In this embodiment, a patterngenerator 105 is configured to generate different patterns for each RZpulse sequence, and drive an array of laser diodes 110, such that eachlaser diode 110 is configured to transmit RZ pulse sequence with aunique pattern to an object 150. It should be appreciated that object150 may be a moveable object or a stationary object. Object 150 may alsobe a soft target, such as clouds, or a hard target, such as a vehicle,building, etc.

Because each RZ pulse sequence has a unique pattern, computing system145 may easily distinguish between the plurality of RZ pulse sequenceseven when transmitted simultaneously. For example, bit error rate can beused for pattern searching algorithms.

In one embodiment, each laser diode may be configured to transmit a RZpulse sequence having a unique pattern at different locations of object150 simultaneously. For example, a first laser diode may transmit a RZpulse sequence at a first location on object 150, a second laser diodemay transmit a different RZ pulse sequence at a second location onobject 150, and so on. By transmitting multiple unique RZ pulsesequences simultaneously to object 150, 3D imaging can be realized.

In another embodiment, each laser diode may transmit RZ pulse sequence,via a scanner or mirror 115, simultaneously to object 150. For example,scanner 115 scans and transmits RZ pulses to various locations on object150. This configuration may also allow 3D imaging to be realized.

A receiver 120 may receive each reflected RZ pulse having its own uniquepattern that bounced back from different locations on object 150. Inthis embodiment, receiver 120 may be a telescope. However, in otherembodiments, depending on design choice, receiver 120 may be any devicethat is configured to receive the reflected pulses.

In order to reduce the optical domain or noise in each of the reflectedsharper pulses, an optical filter 125 is utilized. This embodiment mayinclude an array of photo detectors 130, such that each photo detector130 can detect the respective reflected sharper pulse and its uniquepattern. It should also be appreciated that a single photo detector maybe used in certain embodiments to detect the reflected pulses.

Amplifier 135, which may be a transimpedance amplifier (TIA) in certainembodiments, may amplify each of the detected RZ pulses, and anelectronic filter 140 may be used to remove or reduce the electronicdomain or noise from each of the detected RZ pulses. A computing system145 may then process each of the amplified RZ pulses, each of theamplified RZ pulse sequence having a unique pattern, to determine thedistance between the source (e.g., laser diodes 110) and object 150. Tomake such a determination, computing system 145 uses a reference patternthat may also be generated by pattern generator 105 at the time thepatterns were generated for each of the RZ pulses.Commercial-off-the-self communication bit-error-rate-tester (BERT) mayalso be used for pattern search data processing in some embodiments.

FIG. 2 is a flowchart illustrating a method 200 for transmitting returnto zero pulses, according to an embodiment of the present invention. Theprocess of method 200 of FIG. 2 may be executed by, for example, thecomponents illustrated in FIG. 1 or the computing system shown in FIG.5. The method includes generating a plurality of patterns to beassociated with a RZ signal at 205. At 210, each of the RZ signals ismodulated with a unique pattern to identify each of the RZ signals. At215, each RZ signal is transmitted to different locations on the object.In this embodiment, each of the RZ signals may be transmittedsimultaneously to different locations on the object in certainembodiments, a scanner may be used to direct each of the RZ signals andtransmit each of the RZ signals to different locations on the object.

FIG. 3 is a flowchart illustrating a method 300 for receiving the RZpulses, according to an embodiment of the present invention. The processof method 300 of FIG. 3 may be executed by, for example, the componentsillustrated in FIG. 1 or the computing system shown in FIG. 5. Themethod includes receiving each of the RZ pulses at 305, and reducing anyoptical domain noise in each of the return to RZ pulses at 310. At 315,each of the received RZ pulses is detected and amplified. At 320, theelectronic domain noise in each of the amplified RZ pulses is reducedand transmitted to a computing system at 325.

FIG. 4 is a flowchart illustrating a method 400 for computing thedistance between the source and the object, according to an embodimentof the present invention. The process of method 400 of FIG. 4 may beexecuted by, for example, the components illustrated in FIG. 1 or thecomputing system shown in FIG. 5. The method includes receiving each ofthe RZ pulses at 405 and receiving a reference pattern to identify eachof the RZ pulses based on the unique pattern associated with each of theRZ pulses at 410. A distance between the source and the object iscalculated based on the time of travel from the source to the object andback from the object to the receiver (or source) at 415.

The method steps shown in FIGS. 2-4 may be performed, in part, by acomputer program, encoding instructions for a nonlinear adaptiveprocessor to cause at least the methods described in FIGS. 2-4 to beperformed by the apparatuses discussed herein. The computer program maybe embodied on a non-transitory computer readable medium. The computerreadable medium may be, but is not limited to, a hard disk drive, aflash device, a random access memory, a tape, or any other such mediumused to store data. The computer program may include encodedinstructions for controlling the nonlinear adaptive processor toimplement the method described in FIGS. 2-4, which may also be stored onthe computer readable medium.

The computer program can be implemented in hardware, software, or ahybrid implementation. The computer program can be composed of modulesthat are in operative communication with one another, and which aredesigned to pass information or instructions to display. The computerprogram can be configured to operate on a general purpose computer, oran application specific integrated circuit (“ASIC”).

FIG. 5 illustrates a block diagram of a computing system 500 for 3Dimaging, according to an embodiment of the present invention. System 500may include a bus 505 or other communication mechanism that cancommunicate information and a processor 510, coupled to bus 505, thatcan process information. Processor 510 can be any type of general orspecific purpose processor. System 500 may also include memory 520 thatcan store information and instructions to be executed by processor 510.Memory 520 can be comprised of any combination of random access memory(“RAM”), read only memory (“ROM”), static storage such as a magnetic oroptical disk, or any other type of computer readable medium. System 500may also include a communication device 515, such as a network interfacecard, that may provide access to a network.

The computer readable medium may be any available media that can beaccessed by processor 510. The computer readable medium may include bothvolatile and nonvolatile medium, removable and non-removable media, andcommunication media. The communication media may include computerreadable instructions, data structures, program modules, or other dataand may include any information delivery media.

Processor 510 can also be coupled via bus 505 to a display 540, such asa Liquid Crystal Display (“LCD”). Display 540 may display information tothe user, such as the distance between the source and the object. Akeyboard 545 and a cursor control unit 550, such as a computer mouse,may also be coupled to bus 505 to enable the user to interface withsystem 500.

According to one embodiment, memory 520 may store software modules thatmay provide functionality when executed by processor 510. The modulescan include an operating system 525 and an enhanced pseudo random codemodule 530, as well as other functional modules 535. Operating system525 may provide operating system functionality for system 500. Becausesystem 500 may be part of a larger system, system 500 may include one ormore additional functional modules 535 to include the additionalfunctionality.

One skilled in the art will appreciate that a “system” could be embodiedas a personal computer, a server, a console, a personal digitalassistant (PDA), a cell phone, a tablet computing device, or any othersuitable computing device, or combination of devices. Presenting theabove-described functions as being performed by a “system” is notintended to limit the scope of the present invention in any way, but isintended to provide one example of many embodiments of the presentinvention. Indeed, methods, systems and apparatuses disclosed herein maybe implemented in localized and distributed forms consistent withcomputing technology.

It should be noted that some of the system features described in thisspecification have been presented as modules, in order to moreparticularly emphasize their implementation independence. For example, amodule may be implemented as a hardware circuit comprising custom verylarge scale integration (VLSI) circuits or gate arrays, off-the-shelfsemiconductors such as logic chips, transistors, or other discretecomponents. A module may also be implemented in programmable hardwaredevices such as field programmable gate arrays, programmable arraylogic, programmable logic devices, graphics processing units, or thelike.

A module may also be at least partially implemented in software forexecution by various types of processors. An identified unit ofexecutable code may, for instance, comprise one or more physical orlogical blocks of computer instructions that may, for instance, beorganized as an object, procedure, or function. Nevertheless, theexecutables of an identified module need not be physically locatedtogether, but may comprise disparate instructions stored in differentlocations which, when joined logically together, comprise the module andachieve the stated purpose for the module. Further, modules may bestored on a computer-readable medium, which may be, for instance, a harddisk drive, flash device, random access memory (RAM), tape, or any othersuch medium used to store data.

Indeed, a module of executable code could be a single instruction, ormany instructions, and may even be distributed over several differentcode segments, among different programs, and across several memorydevices. Similarly, operational data may be identified and illustratedherein within modules, and may be embodied in any suitable form andorganized within any suitable type of data structure. The operationaldata may be collected as a single data set, or may be distributed overdifferent locations including over different storage devices, and mayexist, at least partially, merely as electronic signals on a system ornetwork.

One or more embodiments of the present invention pertain to determiningthe distance between a source and an object. Certain embodiments mayinclude generating a plurality of patterns used to identify each of theRZ pulses that are simultaneously transmitted to the object. Thedistance between the object and the source may be calculated based onthe time of travel for the RZ pulses.

It will be readily understood that the components of the invention, asgenerally described and illustrated in the figures herein, may bearranged and designed in a wide variety of different configurations.Thus, the disclosure is not intended to limit the scope of the inventionas claimed, but is merely representative of selected embodiments of theinvention.

The features, structures, or characteristics of the invention describedthroughout this specification may be combined in any suitable manner inone or more embodiments. For example, the usage of “certainembodiments,” “some embodiments,” or other similar language, throughoutthis specification refers to the fact that a particular feature,structure, or characteristic described in connection with an embodimentmay be included in at least one embodiment of the invention. Thus,appearances of the phrases “in certain embodiments,” “in someembodiments,” “in other embodiments,” or other similar language,throughout this specification do not necessarily all refer to the sameembodiment or group of embodiments, and the described features,structures, or characteristics may be combined in any suitable manner inone or more embodiments.

One having ordinary skill in the art will readily understand that theinvention as discussed above may be practiced with steps in a differentorder, and/or with hardware elements in configurations that aredifferent than those which are disclosed. Therefore, although theinvention has been described based upon these preferred embodiments, itwould be apparent to those of skill in the art that certainmodifications, variations, and alternative constructions would beapparent, while remaining within the spirit and scope of the invention.In order to determine the metes and bounds of the invention, therefore,reference should be made to the appended claims.

The invention claimed is:
 1. A space based low power high resolution 3Dimaging docking lidar system using resolution-enhanced pseudo-noisecoding apparatus, comprising: an array of laser diodes includingnon-linear adaptive processor means for generating a plurality of uniquepatterns to be associated with a return to zero (RZ) signal, each laserdiode configured to transmit said return to zero (RZ) signal todifferent locations simultaneously on a reflective moveable ornon-movable object which reflects pulses; a photo detector receiver forreceiving each reflected RZ pulse from different locations on saidobject configured to receive each of the transmitted return to zerosignals, identifying said reflective object, wherein each of the returnto zero signals comprises a unique, pattern to distinguish betweenitself and the other simultaneously transmitted return to zero signals.2. The apparatus of claim 1, further comprising: a pattern generatorconfigured to generate a plurality of unique patterns and drive thearray of layer diodes, such that each of the laser diodes simultaneouslytransmits the return to zero signal to different locations on theobject.
 3. The apparatus of claim 1, further comprising: a scannerconfigured to direct each of the return to zero signals and transmiteach of the return to zero signals to different locations on the object.4. The apparatus of claim 1, further comprising: an optical filterconfigured to reduce optical domain noise in each received return tozero signal.
 5. The apparatus of claim 1, further comprising: an arrayof detectors configured to detect each received return to zero signal.6. The apparatus of claim 1, further comprising: an amplifier configuredto amplify each detected return to zero signal.
 7. The apparatus ofclaim 6, further comprising: an electronic filter configured to reduceelectronic domain noise in each amplified return to zero signal.
 8. Theapparatus of claim 1, further comprising: a pattern generator configuredto generate reference patterns to identify each of the return to zerosignals based on the unique pattern included in each of the return tozero signals.
 9. A method for using a space based low power highresolution 3D imaging docking lidar system using resolution-enhancedpseudo-noise coding for recognizing an object comprising: transmitting,by each of a plurality of non-linear adaptive processor controlled laserdiodes, a return to zero signal to different locations simultaneously onan object; and receiving, by a photo detector receiver, each of thetransmitted return to zero signals, identifying said reflective object,wherein each of the return to zero signals comprises a unique pattern todistinguish between itself and the other transmitted return to zerosignals.
 10. The method of claim 9, further comprising: generating, by apattern generator, a plurality of unique patterns; and driving, by thepattern generator, each of the laser diodes such that each of the laserdiodes simultaneously transmits the return to zero signal to differentlocations on the object.
 11. The method of claim 9, further comprising:scanning, by a scanner, each of the return to zero signals; andtransmitting, by each of the plurality of laser diodes, each of thereturn to zero signals to different locations on the object.
 12. Themethod of claim 9, further comprising: reducing, by an optical filter,optical domain noise in each received return to zero signal.
 13. Themethod of claim 9, further comprising: detecting, by an array ofdetectors, each received return to zero signal.
 14. The method of claim9, further comprising: amplifying, by an amplifier, each detected returnto zero signal.
 15. The method of claim 14, further comprising:reducing, by an electronic filter, electronic domain noise in eachamplified return to zero signal.
 16. The method of claim 9, furthercomprising: generating, by a pattern generator, a plurality of referencepatterns to identify each of the return to zero signals based on theunique pattern included in each of the return to zero signals.